The present invention generally relates to an arterial blood filter. More particularly, the present invention pertains to an arterial blood filter used in an extracorporeal circuit during cardiovascular surgery.
During cardiovascular surgery, the patient""s blood is circulated via an extracorporeal circuit. The patient""s blood exits the body via a venous cannula, which is a flexible tube that is inserted over a vein. The venous cannula is placed either in the superior or inferior vena cava, which are veins that drain blood from the upper body and the lower body and empty into the right atrium of the heart.
Typically, the blood from the body enters a reservoir and is then pumped through an oxygenator with an incorporated heat exchanger. After passing through the oxygenator, the blood enters an arterial filter. The arterial filter is designed to remove air, debris, and aggregated blood elements, and is usually the last component in the circuit through which the blood passes before being returned to the patient. The blood is then returned to the patient via an arterial cannula which is placed in the aorta, and then circulated throughout the patient""s body.
A blood filter should be designed to have low resistence to flow, small priming volume and smooth inside surfaces, and should avoid traumatizing formed blood elements. More importantly, the filter must be able to assist in the removal of air and other undesirable constituents prior to being returned to the patient.
Typically, arterial filters generally consist of a top housing, a bottom housing, and a filter element, and sometimes a cap to hold the filter element in place. However, there are many disadvantages associated with these known filtering devices.
For instance, U.S. Pat. No. 3,827,562 to Esmond discloses a device for the removal of gases, particulate matter and oil primarily from blood after the treatment of the blood in an artificial body device. The filter device utilizes a plurality of filter cloth layers disposed generally parallel to the path of blood flow and supported against collapse by a relatively coarse mesh disposed between adjacent filter cloth layers. The filter layers are disposed in the bottom portion of the housing and completely fill the bottom portion, so that there is no space between the bottom portion of the housing and the filter layers.
The blood enters through an inlet conduit disposed on the side of the housing, with an exit conduit disposed at the bottom portion of the housing and an air conduit located in the top portion of the housing. As the blood enters the device, the blood rests on the top of the filter layers, and eventually sinks through the filter layers, thereby entrapping gases or bubbles contained in the blood. However, the blood that accumulates adjacent the filter cloth is not sufficiently exposed to the air conduit for venting. The blood accumulated adjacent to the filter cloth travels too rapidly through the filter cloth, and hence does not have sufficient exposure to the air vent for removal of air bubbles.
U.S. Pat. No. 4,411,783 to Dickens et al. discloses a blood filter including a filter element comprising an array of layers. The filter element is disposed within a housing and includes a perforated tubular core at its center, and a filter cap covering the upper ends of the core and the filter element. Blood enters the blood filter from a blood inlet tangentially disposed at the top portion of the housing, and flows in a swirling motion outside the filter element and above the filter element cap. However, because of the swirling motion, blood enters the filter element along its outer surface and at too high a rate of speed, which prevents proper air removal.
U.S. Pat. No. 4,919,802 to Katsura discloses a blood filter having a bubble separating section including a generally cylindrical chamber for allowing the bubbles to separate from blood, an air discharging vent at an upper end of the chamber, and an inlet conduit horizontally extending from the chamber for introducing blood into the chamber. However, because the blood is centripetally directed about the filter element, the fluid comes in direct contact with the filter element at high shear rates, and is discharged too rapidly from the filter without subjecting the blood to sufficient air removal.
U.S. Pat. No. 4,490,254 to Gordon et al. relates to a blood filter assembly in which blood enters at the bottom end of the assembly, is directed in a spirally upward path and then passes through a filter medium. After passing through the filter medium, the blood flows downwardly out of an outlet in the bottom end of the assembly. A gas vent is provided at the top end of the assembly for air removal. However, because the blood is centripetally directed about the filter element, the fluid comes in direct contact with the filter element at high shear rates, and is discharged too rapidly from the filter without subjecting the blood to sufficient air removal.
U.S. Pat. No. 4,344,777 to Siposs discloses an arterial blood filter having an internal divergent blood flow path from the inlet to smoothly reduce blood flow velocity and permit separation of air bubbles with minimum trauma to blood cells. The blood is received into the flow cone and the blood flows over the cone and into the filter element. A shield is formed as part of the flow cone, and extends part of the length of the filter element. The shield functions to lengthen the path the air bubbles have to travel before they reach the filter element. However, the blood must travel through complicated paths, potentially disrupting or damaging fragile blood cells.
U.S. Pat. No. 5,462,675 to Hopkins et al. discloses a filter assembly for decreasing fluid hold-up waste and providing uniform flow while maintaining desired flow rates and pressures. The assembly includes a housing, a filter element including first and second end caps and a filter fastened between the end caps, and a sleeve. The sleeve is positioned around the filter and is joined to the first and second caps, thereby forming a single integral unit which is positioned within the housing. However, the filter decreases fluid hold-up waste, but does not promote air removal from the fluid.
A need thus exists for a blood filter that overcomes the disadvantages described above. In particular, there is a need in the art for a blood filter having a blood trap function and a filtering function, both of which assist in the removal of air and other particulates from the blood prior to being returned to the patient.
In light of the foregoing, one aspect of the present invention involves an arterial blood filter. The filter comprises an outer housing having a first section and a second section. The outer housing includes a blood inlet and blood outlet. A vent is formed in one section of the outer housing for discharging air. A filter element is disposed within the outer housing for filtering blood. An inner housing is disposed between the filter element and the outer housing. The inner housing extends substantially an entire length of the filter element and includes at least one opening at a bottom surface of the inner housing.
According to another aspect of the invention, a system for filtering blood is provided. The system includes a blood reservoir for connection to a vein of a patient, a pump for connection to the blood reservoir, an oxygenator for connection to the pump, and an arterial filter for connection to the oxygenator. The filter comprises an outer housing having a top section and a bottom section. The outer housing includes a blood inlet and blood outlet. A vent is formed in the top section of the outer housing for discharging air. A filter element is disposed within the outer housing for filtering blood. An inner housing is disposed between the filter element and the outer housing. The inner housing extends substantially an entire length of the filter element and includes at least one opening at a bottom surface of the inner housing.
Another aspect of the invention involves a blood filter for use in an extracorporeal circuit. The blood filter comprises an outer housing provided with a blood inlet for introducing blood into the outer housing and a blood outlet through which filtered blood exits the outer housing. A blood filter element is positioned within the outer housing to filter blood that has entered the outer housing through the blood inlet. The blood filter element surrounds an exterior space that is in communication with the blood outlet. An inner housing is positioned between the outer housing and the blood filter element and has an axial height at least equal to the axial height of said blood inlet.